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  Thermoplastic formed panel, intermediate panel for the fabrication thereof, and method for fabricating said panel and said intermediate panelUSPTO Application #: 20060105661Title: Thermoplastic formed panel, intermediate panel for the fabrication thereof, and method for fabricating said panel and said intermediate panel Abstract: The invention relates to a thermoformable panel. According to the invention, the panel is composed of thermoplastic fibers forming a nonwoven fabric particularly having double crossed, randomized and thermally bonded webs, pressed under heating to cause a partial “melting” of the fibers, i.e. at least a partial loss of their fibrous phase and change into a viscous or viscoelastic phase, the relative distributions of the fraction of fibers that retain the fibrous phase and the fraction of plastic material that took the viscous or viscoelastic state depending on the depth thereof in the sheet thickness. The invention further relates to a formed, especially a highly embossed panel made of a thermoformable plastic material. The latter may be an intermediate semifinished product of a starting material. The invention also relates to a method for fabricating highly embossed panel. Particularly, the invention relates to a formed, especially a highly embossed panel and to the method for fabrication thereof, which highly embossed panel finds use in the automotive, naval, aerospace, railway and building industries, for the fabrication of interior or exterior coverings or structural members. (end of abstract) Agent: Serafini Associates - La Jolla, CA, US Inventor: Paolo Steinbach USPTO Applicaton #: 20060105661 - Class: 442327000 (USPTO) Related Patent Categories: Fabric (woven, Knitted, Or Nonwoven Textile Or Cloth, Etc.), Nonwoven Fabric (i.e., Nonwoven Strand Or Fiber Material) The Patent Description & Claims data below is from USPTO Patent Application 20060105661. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The invention relates to a thermoformable panel made of a thermoplastic material. [0002] Thermoformable thermoplastic panels or sheets are widely known in many variants and used in various fields for the fabrication of different products. [0003] These sheets may be particularly used in the fabrication of formed, especially highly embossed panels with many different well-known thermoforming techniques. These formed, especially highly embossed panels may be used in several fields, e.g. in building, either for interior and exterior finishing, or as a material for building structures, like formworks used to contain concrete or the like and/or as acoustic isolators. The fabrication of furnishings, i.e. furniture or the like is also included in the field of application of thermoformed panels, and particularly these panels are widely used in the automotive industry, and in the production of vehicles in general, i.e. ground, naval or aerospace vehicles, for instance in the fabrication of interior panels, like trim elements of automotive vehicles or the like. [0004] In the naval, aerospace or railway fields, thermoplastic panels may be used either as trim materials for coverings or the like, in the same manner as for automotive vehicles, or as structural members for the fabrication of partitions, bulkheads, roofs, floors, etc. In these fields, and particularly for modern ships or high-speed trains, the use of plastic panels is particularly advantageous, due to the considerable lightness thereof. [0005] The panels designed for the above mentioned purposes are required to have several aesthetic, physical, mechanical, formability and cost features that are often in contrast with each other and hardly obtainable to the same extent. Obviously, these panel features also affect the features required of the thermoformable sheets wherefrom panels are obtained. [0006] While considering the need of minimizing costs, the panels shall be as light as possible, while having high mechanical strength properties. Conversely, these panels, as well as the sheets whereof they are made, shall ensure high deformability or formability because, particularly in the automotive field, the requested three-dimensional shapes include considerable shape variations, hence sheets shall allow deep drawings during panel forming. While lightness requires relatively rigid structures, having precise symmetries and anisotropies, which means that sheets shall exhibit a suitable internal structure for forming grids, interlacements, leases which, as the material is compacted, generate stiffening ribs or knots, this need is in conflict with some of the required mechanical properties, especially with the high embossing required of sheets. Particularly in plastic materials, the fibrous phase, i.e. including plastic molecule agglomerations requires an elastic or almost elastic condition of said material, whereas the need of allowing a high three-dimensional embossing requires a good flowability of thermoplastic molecules, i.e. a phase that may be defined as viscous or viscoelastic, and may be typically obtained by heating the material to a temperature below the melting point, which causes an effect of a transition in the viscous or viscoelastic state, instead of melting. [0007] The elastic condition and an important substantially fibrous phase allow the material to be properly stiffened, and improved in terms of tensile, torsional and compression strength. Certain particular fields of use require also that when the material is broken, it is free from sharp edges (e.g. like in traditional glass breaking arrangements). There is therefore a need of a material which has at the same time a resilient and an elastic behaviour and showing also a so called "ductile breaking", i.e. without forming sharp edges at the broken region. In other fields, like in building, the material is required to have an optimal behavior in terms of mailability. Concerning mailability, the ideal behavior consists in allowing nail penetration without causing veining, breaking or cracking, branching off the penetration point. As an ideal behavior, the material is required to receive the nail and form a corresponding hole area, the material being only substantially broken at the nail hole area. Also, considerable advantages may be obtained by using a material that may retain a certain elasticity in the nail penetration area, to at least partly close the nail penetration hole, once the nail is removed therefrom, to obtain a certain self-repairing action in the sheet or in the panel formed therefrom. Therefore, the material is advantageously required to be able to expand at least partly to at least partly reduce or almost wholly or wholly close the hole. [0008] The above particular needs are in contrast with rigidity, flexibility and mechanical strength needs that require a more resilient structure of the panel material, and of the sheet material wherefrom the panel is obtained by a forming process. [0009] Panels are often required to be covered with outer layers having both aesthetic and protective functions or other field-specific functions. In this case, the material of the panel and the sheet wherefrom the panel is made, shall be chemically and physically compatible with usual covering materials, i.e. for example thin sheets such as adhesive materials to improve fixation of covering layers. In order to increase formability, panels are also often laminated on the backside with nonwoven fabrics of synthetic or natural materials. Restrictions are also provided regarding the type of plastic which forms the panels and sheets. These restrictions are further limited due to the increasing interest for environment protection, which requires sheets and panels to be preferably made of materials that are as recyclable as possible. Particularly, sheets and panels should allow an at least mechanical fixation of the covering layer fibers or surfaces within the sheet material, by partial embedding thereof in the matrix of the surface layer of the sheet plastic material. [0010] Depending on the field of application and use of the panel, other physical, aesthetic and mechanical properties may be also required. In certain instances, an at least partial surface compliance is required of the panel, i.e. a certain softness thereof. This may be also desired in certain particular areas of the panel. On the other hand, such softness shall coexist with a certain mechanical strength and rigidity and with the other properties mentioned above. In prior art, this is obtained by forming closed- or open-cell foamed sheets. However, these sheets often do not provide panels having high mechanical strength properties, and foam layers must be backed by supporting or stiffening layers. On the other hand foams often collapse during forming. [0011] If mechanical strength requirements are so high that they cannot be provided by a single-layer sheet, even when the latter is not made of foam, the sheet must have a composite, i.e. multilayer construction, and include at least one stiffening layer made of thermoformable plastic or natural materials or stiffening lattice structures, and this obviously limits sheet formability. [0012] Further characteristics are associated to the requirement of thermal and acoustic insulation properties, as well as tactile effects, e.g. for panels required to be warm to the touch or the like. [0013] In prior art techniques for fabricating thermoformed products as described hereinbefore from thermoformable sheets, polyolefin sheets are currently used, which are mixed with fillers like wood flour, talc or the like and natural fibers, such as vegetal fibers or plastic fibers, to remove or reduce the generation of sharp edges or tips upon fracture. Adding talc to the panel material causes a fragile behaviour of the panel [0014] The above arrangement, resulting in only partly satisfactory results, also requires sheets to be previously processed to mix thermoplastic materials with fibers and fillers, and fibers are often not optimally embedded therein, causing a non uniform quality of the sheets. Also, natural fibers shall be treated against microbiological and mycological agents which cause degeneration and decomposition thereof, as well as the generation of unpleasant odors. Moreover, these degeneration effects cannot be completely obviated and the sheet is always exposed to quality degeneration, also due to atmospheric agents like moisture or direct exposure to water. [0015] The methods for forming sheets and applying various covering layers thereto, include various combinations. Sheets are typically obtained by extrusion, regardless of their being made of a foamed or compact material. A general draw back of extrusion consist in the fact that during extrusion it is very difficult to distribute uniformly the fibers in the mass of the polymeric material. Extrusion exercises a shearing stress on the fibers which causes a breaking of the long fibers. This reduction in length of the fibers has a direct consequence a reduction of the resilience of the material. Furthermore the fibers are admixed to the polymeric mass during extrusion and this fact causes an anisotropy of the fibers distribution in the polymeric mass and in the extruded product leading to local differences of specific weight within the extensions of the extruded product and thus in differences in the mechanical behavior at different points or regions of the extruded product. [0016] Forming is carried out by heating and compression inside a mold. Various methods are used, such as thermocompression or mold and countermold forming, hydraulic or pneumatic pressure against a rigid surface of a mold, vacuum forming or suction of the sheet against a rigid forming surface or hybrid methods which include the above compression methods, at least for certain areas or in combination with each other. [0017] It is further widely known to apply, when required, covering layers, adhesives or other layers of material during the forming process. [0018] Prior art alternative methods are to be also mentioned herein, particularly for the fabrication of panels formed with deep recesses and/or ridges, which methods consist in injection molding. As compared with the panel fabrication methods including flat sheet forming, these methods are considerably more expensive and complex, particularly as regards the fabrication of panels covered by or composed of multiple layers, and not suitable for integration of a fibrous structure therein. [0019] Especially the last kind of process leads to materials having a fragile behavior relatively to breaking and usually there are limitations relatively to the different materials which can be used for lining the panel, particularly but not limited to a process known in the art as low pressure molding. [0020] Document U.S. Pat. No. 4,258,093 discloses a panel having a three dimensional shape, typically of concave-convex form and having sufficient rigidity to maintain that form. Such panels are molded from nonvowen, needlepunched fabrics containing certain ethylene-vinil acetate fibers in admixture with fibers of a higher melting point polymer. Molding is accomplished by heating the fabric to a temperature whereat the ethylene-vinyl acetate fibers soften or melt but below the melting point of the other fibers and thereafter pressing the fabric between the mating surfaces of a mold pair and allowing the ethylene-vinyl acetate fibers to solidify and cool while in the mold. [0021] U.S. Pat. No. 4,818,586 discloses a similar panel made of nonwoven textile fibers, The synthetic thermoplastic fibers are also needlepunched to produce a carpeting material which can then be directly utilized or thermoformed to retain the desired shape. [0022] EP 0174813 discloses a three dimensional molded article suitable for use as a fibrous surface panel for automobile trunk compartments and the like. These articles are produced by molding a heated non woven web formed of a blend of relatively high melting fibers and relative low melting fibers. The low melting fibers form a multiplicity of bonds which impart shape retentive rigidity to the non planar three dimensional web. The low melting fibers present at one surface of the web have a fibrous form, while the low melting fibers present at the opposite surface of the web have portions which exhibit a non fibrous fused form and form said bonds. [0023] U.S. Pat. No. 5,362,546 discloses a three dimensional non woven fabric with a thermally activated adhesive surface. The fabric is used as a facing fabric for covenrign a fibrous mat. The fabric comprises two adjoining fibers layers, namely an adhesive layer including bod forming fibers fusible at a predetermined temperature and a facing layer of fibbers having a considerably higher melting temperature than the bond-forming fibers. The fibers of both layers are mechanically engaged one with another and are arranged flatwise in bundles interconnected at junctures by protuberant fibers packings disposed in a staggred relationship throughout the fabric. Bond-forming fibers are concentrated in the apex portions of the fiber packings to form thermally activated adhesive surface. These non woven fabric facing fabric layer can be used in combination with a non woven molded fibrous mat. [0024] DE 198 12 925 discloses a three dimensional formed article comprising a needle punched non woven mat formed by two or more layers structurally neddled together. A first layer comprises a blend of polypropylene fibers and polyethylene fibers and a second or further layer comprises a blend of polypropylene fibers and polyethylene fibers. Both layers are bonded together by needlepunching and by melted fibers or part of the fibers of the polyethylene fibers component of both layers. Continue reading... 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